What kinds of films are suitable for use in solar greenhouses and what are their characteristics?

There are many kinds of films suitable for solar greenhouse. According to the different resin raw materials, it can be divided into polyethylene (PE) film, polyvinyl chloride (PVC) film and vinyl acetate (EVA) film; According to its performance characteristics, it can be divided into ordinary film, long-life film, drip free film, long-life drip free film, diffuse reflective film, composite multi-functional film, etc. The properties of these films have their own characteristics and strengths. Combined with the current production needs, this paper introduces several commonly used films for reference when building greenhouses.
Types and characteristics of films
(1) Polyethylene ordinary film (PE)
The light transmittance of the new film is about 80%; Weak dust absorption, without the phenomenon of excessive dust absorption (tackiness) caused by plasticizer precipitation of polyvinyl chloride (PVC) film. It has strong low temperature resistance, low temperature brittleness is - 70 ℃, and it can still maintain softness at - 30 ℃. The relative density is 0.92g/cm3, and the infrared transmittance is more than 70%. The heat preservation performance at night is poor, not as good as PVC film. The fog drop property is heavy, and the weather resistance is poor. The service cycle is 4-5 months. It is not sun resistant, and the high temperature softening degree is 50 ℃. Therefore, it is not suitable for covering cultivation in high temperature season. It can be used for covering cultivation in early spring and late autumn. It is not easy to bond after tearing. At present, there is no suitable repair adhesive, and it can only be heat sealed when splicing.
(2) Polyethylene long-life film
It is made of polyethylene as the base resin by blowing after adding a certain proportion of ultraviolet absorber, anti-aging agent and antioxidant. The weather resistance is good, and the service life is 1.5~2 years. The thickness is 0.1~0.12 mm, the amount of film used per 667 m2 is 100~120 kg, and the breadth varies from 1 m, 1.5 m, 2 m, 3 m, 3.5 m, and 4 m, that is, the width of a single breadth after opening is 2 m, 3 m, 4 m, 6 m, 7 m, and 8 m. The application area has expanded rapidly in recent years. Although the one-time investment is larger, it has a long service life and can be used for almost four crops, which is more economical than ordinary PE film.
(3) Polyethylene drip free long-life film
It is made of polyethylene as the basic resin, added with anti-aging agent and drip free additive, and then blown. The weather resistance is good, and the service life is more than 1.5~2 years. No condensation. The thickness is 0.1~0.12 mm, the dosage is 100~130 kg per 667 m2, and the width varies from 1 m, 1.5 m, 2 m, 3 m and 3.5 m, which is suitable for various greenhouses and greenhouses. It can also be used as a two curtain covering in greenhouses and greenhouses.
(4) PVC common membrane
The agricultural film is made of PVC as the basic resin. It is resistant to high temperature and sunlight. Its insulation at night is better than that of polyethylene film, and it is resistant to aging. The fog drops are light. After the film is torn and broken, it can be bonded with adhesive, which is convenient to repair. The thickness is 0.1~0.12 mm, and the width and diameter are 1 m, 2 m and 3 m. The dosage is 130 ~ 150kg per 667m2, and the relative density is 1.25 g/cm3. The coverage area of the same amount is 24% more than that of the polyethylene film with the same thickness. The new film has good light transmittance. However, with the extension of the coverage time, the plasticizer gradually precipitates, and the film surface has a sticky feeling, so the dust absorption is strong, and it is difficult to clean. The light transmittance is quickly reduced, and the low temperature resistance is poor. The low temperature brittleness is - 50 ℃, and the hardness is - 30 ℃; PVC film is more suitable for areas with small wind sand and less dust, especially for northern areas where night insulation cultivation is required.
(5) Multifunctional membrane
With polyethylene as the basic resin, a variety of additives are added, such as drip free agent, heat preservation agent, anti-aging agent, etc., to make a film have a variety of functions, such as longevity, drip free, heat preservation, etc., to achieve multiple effects at the same time. In terms of processing technology, one is to evenly mix the basic resin with various additives and blow to form a film; the other is to form a composite film, such as a three function composite film, in which a drip free agent is added to the inner layer and an ultraviolet absorber is added to the middle and outer layers to form a multi-functional composite film. The thickness is 0.06~0.08 mm, the service life is more than 1 year, the transparency and thermal insulation are good, the temperature rises quickly in sunny days, and the thermal insulation effect is available at night. It is suitable for large, medium and small greenhouses, greenhouses, and as a second curtain. Due to its thin thickness, the film coverage area per unit weight is large, and the consumption per 667 m2 is only 60~100 kg.
(6) Diffuse reflective film
With polyethylene as the base resin, a certain proportion of diffuse reflective crystal nucleus is added. When the direct sunlight penetrates this film, it will be converted into flat light under the effect of diffuse reflective crystal nucleus, and will be more evenly transmitted to all parts of the greenhouse, reducing the transmittance of direct sunlight. This can not only reduce the peak temperature in the shed around noon, reduce the damage of high temperature to crops, but also help the uniformity of plant growth in the shed. At the same time, the heat preservation at night is good, and the accumulated temperature of greenhouse is higher than that of PE and PVC ordinary agricultural film.
(7) Polyethylene dimming film (light conversion film)
A new type of plastic film was blown from low density polyethylene (LDPE) with light conversion agent. It can convert the ultraviolet light in natural light into red light and infrared light, and reduce the ultraviolet light that is not beneficial to plants. The increase of red light and infrared light can improve the photosynthetic utilization rate of plants, strengthen photosynthesis, and increase the indoor air temperature and ground temperature in the shed. The agricultural film has the characteristics of long life, aging resistance and good light transmittance. The thickness is 0.08-0.12mm, the amplitude diameter is 1-5m, the tensile strength is greater than or equal to 13mPa, the elongation at break is greater than 305%, and the right angle tear strength is greater than or equal to 50kg/m. The service life is more than 2 years, the light transmittance is more than 85%, and the warming effect is not significant under weak light.